Here are some reasons why I think this is one of the more misunderstood issues within the worship life of the congregation:
Reason #1 - The liturgical calendar vs. the secular calendar. The liturgical calendar is the church's seasonal approach to the selection of hymns. Liturgically minded churches are churches that take seriously the worship themes of the particular liturgical season the church is experiencing. For example, Advent (the four Sundays leading up to Christmas) is not a season to celebrate the birth of Christ but instead is a season in which to repent and wait expectantly for Christ's coming/2nd coming. Liturgically speaking, the Christmas season begins on Christmas Eve and lasts for 12 days (as in "The Twelve Days of Christmas" song) until Epiphany (January 6.)
The secular calendar wants Christmas to begin sometime around Halloween, or at the latest, on the famous "Black Friday" shopping day. The church has said, "wait just a minute!" Christ's birth celebration isn't until the Christmas season. We need the four weeks before Christmas to be a time of preparing for his coming, not a time of celebration.
Reason #2 - Even though United Methodists have deep liturgical roots thanks to our founder, John Wesley and our Anglican heritage, not all pastors are liturgically minded. Some pastors are biased against the liturgical calendar because it feels too "Catholic" even though good liturgical practice isn't confined to the Roman Catholic Church. Liturgy is practiced widely by many strands of Christendom. In fact, several newer evangelical churches are beginning to reclaim the ancient/orthodox liturgical heritage which utilizes the liturgical seasons, the rich symbolism, and the more orderly approach to the Christian faith. How ironic that when some mainline denominational members have given up on liturgy, several new and growing churches are discovering how liturgy is connecting to younger generations who are hungry for this type of liturgical expression in worship.
On the other hand, there are also other United Methodist pastors who have used good liturgical practice in their churches and many UM congregations have enjoyed being faithful to the particular seasons in the church year and being distinctive from the secular culture. If some of these liturgically rooted church members would visit a church that has little sense of liturgy, it would feel strange to them.
Reason #3 - There is a sense among some church goers that pastors and worship leaders should choose the hymn favorites of the congregation. I've actually heard of churches who have conducted surveys on their favorite hymns and the pastor has inserted hymns into worship based on this survey. Well, that's OK if you're not interested at all in matching up the scripture readings for a particular Sunday with the appropriate hymns.
It's ironic that many folks who want favorite hymns are also the same folks who hold great reverence for the Bible, and yet personal hymn preferences are often chosen over against the theme of a given Sunday's scripture readings. Again, the Advent and Christmas seasons are good examples of this! The rule of thumb in choosing hymns for worship is that the theme of the scriptures for that Sunday always rule the roost.
Other thoughts: Having said all of this, believe me, I have my own favorite hymns that I would like to sing more than 2 times a year. Maybe my favorite hymn will be selected but it first has to meet the liturgical and scriptural theme test before it even becomes a candidate.
And last but not least, some of the lesser familiar hymns are chosen less for their singability and more for their very appropriate and deeply rich lyrics. And sometimes, the melody will grow on you and this unfamiliar hymn ends up helping you to worship on a deeper level for that Sunday.
For the liturgical calendar, this website, The Voice, is an excellent resource for folks who want to grow in their appreciation for the seasons of the church year.